Abstract:

【Objective】 Understanding soil nitrogen transformation and supplying process is the key for optimizing crop cultivation and nitrogen managements. 【Method】 In this paper, soils were sampled from a 5-year-long field experiment to study the effects of different soil surface mulching on soil organic nitrogen accumulation and mineralization in dryland of northwestern China. 【Result】 The results showed that compared to conventional cultivation, long term surface mulching with straw increased soil nitrogen mineralization potential but decreased mineralization rate. Mulching with plastic-film decreased nitrogen mineralization potential, but increased mineralization rate. The nitrogen mineralization potential for the conventional cultivation, straw mulching and plastic film mulching was 25.0-29.7, 23.2-25.9 and 23.3-26.2 mg?kg-1, respectively. Without N application, straw and plastic-film mulching increased soil organic nitrogen and light fraction organic nitrogen contents. When N was fertilized, straw mulching could increase soil organic nitrogen and light fraction organic nitrogen contents, while plastic-film mulching decreased their contents. At N rate of 240 kg?hm-2, the organic nitrogen content was 1.03, 0.95 and 0.96 g?kg-1, and the light fraction organic nitrogen content was 51, 35 and 37 mg?kg-1 for the conventional cultivation, straw mulching and plastic film mulching, respectively. 【Conclusion】 It is concluded that surface mulching with straw causes soil to immobilize more mineral N into mineralisable organic N, while with plastic film is not beneficial to organic nitrogen accumulation. Therefore, in order to increase crop yield, more nitrogen fertilizer is needed or supplemental N fertilizer should be applied at the key nitrogen requirement stage under straw mulching cultivation as it could increase soil N supply capacity. For plastic film mulching, more attention should be paid to application of organic fertilizer.

Key words: straw mulching, plastic-film mulching, nitrogen mineralization potential, light fraction organic nitrogen